As the chances dim for finding Malaysia Airlines Flight 370's "black box" flight recorders before the batteries in their locator beacons run out, Malaysian and Australian leaders sought to inject new momentum into a search of the southern Indian Ocean that has yet to find plane wreckage.

Malaysian Prime Minister Najib Razak met aircrews involved in the multinational search for Flight 370 at Pearce air base, near Perth, on Thursday. The visit is Mr. Najib's first to Australia since the focus of the search swung...